1. Field of the Invention
The present invention relates to a field effect transistor, and more particularly, to a field effect transistor using graphene in a channel layer.
2. Description of the Related Art
Kostya Novoselov and Andre Geim were first to discover how to fabricate graphene, which consists of two dimensional carbon atoms in a hexagonal structure, by mechanically exfoliating graphite, and have reported field effect characteristics exhibited by the graphene, numerous attempts of fabricating highly efficient transistors with high operating speed using graphene are being made.
Graphene is a carbon nanostructure that has a two-dimensional shape, high charge mobility of approximately 15,000 cm2/Vs, and excellent thermal conductivity. Thus, the graphene is considered as a next-generation material for replacing silicon that is currently being used in field effect transistors. Large area integration is difficult in the case of using carbon nanotubes in the formation of transistors. However, if graphene material is used in the formation of transistors, a device can be easily fabricated using conventional semiconductor fabricating techniques, and particularly, large area integration can easily be achieved.
However, graphene is a semi-metal having a zero energy band gap, that is, having no energy band gap. Therefore, graphene has a very large off current, and thus an on/off ratio of an operating current is very small. The maximum on/off ratio of a field effect transistor using semi-metallic graphene as known hitherto is approximately 6. Such a low on/off ratio works against large integration and high-speed operation of a field effect transistor.
Recently, various attempts have been made to increase the on/off ratio of the operating current of a field effect transistor. One of those attempts is fabrication of a semiconductor graphene having a proper energy band gap for an effective field effect. Zhang et al. have simulated nanoribbon tunnel transistor model using a semiconductor graphene and suggested a method of increasing an on/off ratio of a field effect transistor using graphene. On the other hand, Lemme et al. have fabricated a non-volatile field effect switching device having a very high on/off ratio by changing the chemical composition of graphene. Accordingly, a graphene layer having a energy band gap is embodied by ridding of the symmetry of a graphene crystal structure exhibited by lattice mismatch between graphene and a substrate, by forming a nanoribbon shape pattern, or by changing the chemical composition of graphene.
However, according to the suggested methods described above, it is difficult to embody graphene in the size of several nano meters, and with excellent quality. Thus, despite of the excellent characteristics of graphene, the integration of graphene to a semiconductor device hasn't been successfully accomplished yet.